Many believe that January was named after the Roman god "Janus". The months of the Gregorian calendar, widely used today, derive their names from Roman mythology, emperors, and Latin. January is named after Janus – the Roman god of beginnings, endings, transitions, and doors.

Janus is often portrayed with two faces – one looking to the past and the other to the future. This idea perfectly symbolises the start of a new year. January replaced March as the first month of the Roman year by 153 BCE – Before the Common Era.

However, there's also widespread belief that the roots of the name "January" actually lie in the Latin word "ianua", meaning door. The name reflects the idea of opening a new door as the new year begins.